Substance use disorders (SUD) in adolescents represent a significant burden of morbidity and cost to society. Adolescents with SUD exhibit impairment in a variety of cognitive domains. In addition to potentially affecting school performance and developmental milestones, cognitive impairment may affect the ability to participate in and benefit from SUD treatment. Given that neuromaturation continues during adolescence, adolescents may be more vulnerable to the neurocognitive sequelae of drugs but may also be more malleable in response to cognitive training. However, to our knowledge, cognitive training has not been tested in adolescents with SUD. The proposed theoretically driven cognitive training intervention (Working Memory Training) targets working memory (WM), and has been shown to increase WM capacity in youth with poor WM skills and ADHD, and to transfer to other cognitive domains, which is rarely observed in training studies. WM is a critical cognitive function whose core component is the 'central executive' (set of executive functions), and is a necessary building block for the performance of other functions. Supporting the potential to enhance SUD treatment outcomes, WM Training reduced drinking and decreased delay discounting (measure of impulsivity that predicts SUD outcomes in adolescent marijuana users) in adults with SUD. In this randomized controlled study, SUD adolescents with marijuana as the primary substance of abuse being treated at Mountain Manor Treatment Center will be assigned to an experimental group who perform computerized WM Training (TRAIN) or an active control group who perform a control version of the computerized program that does not challenge WM (CON). The 30-session intervention will be layered onto standard intensive outpatient treatment. A battery of state-of-the-art cognitive assessments will be administered before and after training, and SUD treatment outcome measures will be included as secondary outcomes. Specific Aim 1 is to test the hypothesis that TRAIN will improve on the trained working memory tasks across training sessions. Specific Aim 2 is to test the hypothesis that TRAIN will show greater improvement on non-trained cognitive tasks relevant to drug use/SUD treatment outcomes and school performance, relative to CON. Specific Aim 3 (secondary) is to test the hypothesis that TRAIN will show decreases in drug use and associated psychosocial functional impairment, and increased treatment engagement, relative to CON. The collaboration between an academic scientist and a community-based treatment program is innovative and ideal for developing and testing this novel intervention layered onto standard SUD treatment, with the goal of real-world implementation/dissemination. In addition to the broad implications of improved cognitive function during this critical developmental period, establishing the effects of training on cognitive functions is the first step in the systematic study of training effects on functional SUD treatment and academic achievement outcomes. The mechanistic approach will also enhance scientific understanding of learning capacity and malleability of specific cognitive processes in response to training.